This invention relates to electronics, and more specifically, to an improved technique of measuring parameters within Silicon on Insulator (SOI) and similar devices.
FIG. 1 shows an exemplary prior art configuration of two semiconductor devices 102 and 103 configured with other elements to form a half bridge circuit. The devices may be MOS devices, SOI, or other type. The devices are typically manufactured using known techniques in which the various required layers are deposited on a substrate 201 as shown in FIG. 2. Devices 102 and 103 are each usually fabricated on a chip, and border 125 represents the external boundaries of the chips.
As FIG. 1 shows, one standard application includes the use of external capacitors 105 and 106 in order to measure the output of the half bridge. A sensing lead 107 is usually connected outside of the chip on which the SOI devices 102 and 103 reside. The sensing lead may be used for taking measurements using standard equipment. The remainder of the external elements, inductor 108, capacitors 109 and 115 and resistor 110, are arranged to form a standard resonant output circuit.
In operation, high voltage capacitor 105 transfers AC signals to sensing lead 107 and such signals are sent to a measurement device in order to monitor operation of the SOI devices from an external piece of equipment. While the arrangement is basically satisfactory, the use of external components increases the cost and decreases the reliability.
The external monitoring is required in a variety of applications. For example, it is desirable in some switching circuits to maintain operation of the device in what is termed the soft switching region. The only way to accomplish this objective is to monitor the operation of the device and provide correction if the hard switching region is approached.
In view of the foregoing, it would be desirable to construct a sensing apparatus that does not require so many additional components. It would also be desirable to minimize manufacturing costs of such devices. It is also a desirable object to eliminate the need for an additional external capacitor.
The above and other problems of the prior art are overcome in accordance with the present invention, which relates to a technique of implementing the required capacitor for sensing without the additional cost and connections typically required in the prior art. More specifically, a separate sensing lead is run from the substrate of the device to an external pin. The inherent residual capacitance between the substrate and the drain is utilized as the sensing capacitor. This residual capacitance is usually deemed an unwanted parasitic capacitance. Applications include utilizing this internal sensing capacitor to control logic gates, to regulate or control external devices, or to maintain a device in the soft switching region. In alternative embodiments, the inherent capacitance between the substrate and other portions of the device (e.g. the gate or the source) may also be used.